Method of recognizing a ventricular cardiac pathological condition for automatic defibrillation purposes, and monitor-defibrillator for implementing said method

ABSTRACT

Procedure to recognize a ventricular cardiac pathological condition in view of an automatic defibrillation and monitor/defibrillator to implement the procedure 
     Procedure to recognize a ventricular cardiac pathological condition characterized in that after an analog preprocessing, the ECG signals are continuously sampled and digitized, then digitally processed by basic periods in such a manner as to periodically measure distinct basic values according to three criteria of zeros Z, of cardiac frequency FC and of arrythmia RR, then to individually allocate to each value a probability weighting according to a weighting scale specific to each criteria, to proceed to sum these basic values to establish an overall probability over a given duration utilized to determine the triggering of a recognition alarm of a cardiac pathological condition. The invention is of particular interest in cardiology in the medical industry.

FIELD OF THE INVENTION

The present invention concerns a procedure to monitor, detect, and toautomatically recognize a dangerous cardiac pathological condition in apatient such as a ventricular fibrillation or a ventricular tachycardiain order to sound an alarm and perform a semi-automatic defibrillation.

This invention also concerns means to implement the procedure as amonitor-detector-defibrillator.

BACKGROUND OF THE INVENTION

The monitoring of the cardiac activity is necessary in all seriouspathological and cardiac cases and in all emergency cases inasmuch asthe monitoring allows gathering of information on the momentarycondition of the patient.

Additionally, the patients and sick susceptible to cardiac disturbances,and notably to disturbances in the cardiac rhythm, necessitate attentivemonitoring depending on the seriousness of their condition.

Actually, arrhythmia generally leads to serious disturbances that may,in certain conditions, lead to the fibrillation of the myocardium, anextremely serious condition that only an electric defibrillation shockcan modify.

A fibrillation corresponds to a total desynchronization of theexcitation of the cardiac fibers, caused by excitation loops that closeon themselves. A self-sustaining movement is created in these loops,called reentrant loops, preventing all new excitation of the cardiacmuscle.

A local fibrillation in the auricles (auricular fibrillation) is notdeadly and may be reduced by an electric shock.

Localized in the ventricles, this fibrillation (ventricularfibrillation) completely stops the functioning of the heart. Indeed, themechanical contraction of the heart practically no longer occurs. Thistotal hemodynamical ineffectiveness causes death in the three to fiveminutes following the onset of the disturbance because of a lack ofcerebral irrigation. Only a defibrillation electric shock canresynchronize all of the cells of the heart.

This treatment consists in applying through the thorax, by twoelectrodes, a short duration current of a few tens of amperes at a fewthousands of volts for a few milliseconds resulting from the dischargeof a capacitor.

Since a few years ago, the defibrillators have been equipped with acardiac monitor to visualize the signal of the electrocardiogram,abbreviated ECG, before and after the defibrillation shock.

Actually, ventricular fibrillation is responsible for most of the deathsoccurring during the course of the pre-hospitalization phase ofmyocardial infarction, without rapid intervention and appropriateemergency equipment. Indeed, present arrhythmia detectors are complex,not transportable, and necessitate the presence of a physician torecognize the fibrillation pathology.

SUMMARY OF THE INVENTION

The first goal of the invention is thus to provide emergency equipmentthat is simple, autonomous, and light, which consumes little energy andis capable of detecting and automatically recognizing a ventricularfibrillation condition in view of sounding an alarm, thus rendering thepresence of a physician non-indispensable for the recognition offibrillation.

Another goal is to extend the recognition to other hazardous pathologiessuch as ventricular tachycardia where the cardiac frequency is greaterthan 140 beats per minute, which presents recognition criteria is commonwith those of fibrillation and also necessitates an electric shock forits treatment.

In this manner, one of the goals of the present invention consists inproposing a monitor-detector capable of recognizing ventricularfibrillation as well as ventricular tachycardia.

A related goal of the invention is the ability to deliver QRS complexdetection data correctly synchronized with the electrocardiogram due tothe importance of the timing of the electric shock for ventriculartachycardia.

Another goal of the invention concerns the possibility, as soon as thealarm is sounded, to be able to prepare the electric shock and topropose a decision to shock, which means placing the associatedemergency defibrillator in condition to deliver the shock as soon as theoperator validates the proposal, thereby notably shortening theintervention delay.

Yet another goal of the invention concerns the possibility of anautomatic defibrillation decision after an additional analysis.

An additional goal of the invention is the ability to function inreal-time.

The last goal specified consists in conceiving a monitor-detector whosefunctioning must produce the fewest false negatives corresponding tomissing detections and the fewest false positives corresponding toexcessive detections.

To attain all of these goals, it was necessary to identify and resolvemany difficulties in the automatic detection of fibrillation andventricular tachycardia, to remedy them and to conceive an entireprocedure for the analysis and recognition of the pathology startingfrom the electrocardiogram signals.

Notably, it was necessary to overcome the following significantdifficulties:

research and study the choice of the analysis and recognition criteria;

eliminate or minimize all of the parasitic signals hindering detectionand identification such as the induced, interfering or associatedequipment coupling signals, background noise, line noise, ambient radiofrequency noise and stimulation impulses;

creating an analysis and recognition computer;

establishing, for each criterium, an increasing probability scale.

To this effect, the present invention concerns a procedure to monitor,to detect and to identify, from an electrocardiological signal, acondition of ventricular fibrillation or rapid ventricular tachycardia,characterized in that after analog preprocessing, the ECG signals arecontinuously sampled and digitized, then digitally processed in basicperiods to provide a periodic measurement of individual basic valuesaccording to the three criteria of zeros Z, cardiac frequency FC andarrhythmia RR, then to individually allocate to each value a probabilityweighting according to a weighting scale specific to each criterium, toproceed with the summation of these values to establish a basicprobability linked to a basic period of analysis and to use the basicprobability of a basic period of analysis and measurement to join it tothe preceding probability in such a manner as to establish an overallprobability used to determine the triggering of a recognition alarm of apathological cardiac condition.

BRIEF DESCRIPTION OF THE DRAWINGS

The technical characteristics and other advantages of the invention areconsigned in the following description, given as example only and notlimited by a specific embodiment in reference to the accompanyingdrawings, in which:

FIG. 1 is an enlarged waveform of an electrocardiogram;

FIG. 2 is a normal electrocardiogram, meaning a waveform ofelectrocardiographical signals in the case of normal cardiac activity;

FIG. 3 is a normal electrocardiogram showing waveforms corresponding toextra systoles;

FIG. 4 is an electrocardiogram of a ventricular fibrillation condition;

FIG. 5 is an electrocardiogram of ventricular tachycardia;

FIG. 6 is a synoptic diagram of the procedure to detect a hazardouspathological cardiac condition according to the basic embodiment of theinvention;

FIG. 7 is a synoptic diagram of the procedure to detect a hazardouspathological cardiac condition according to a basic embodiment improvedby the automatic shock decision and an additional analysis;

FIG. 8 is the synoptic diagram of the procedure to detect a hazardouspathological cardiac condition according to an embodiment withoutacquisition circuit;

FIG. 9 is a double graphic explaining the analysis criterium called"zero criterium";

FIG. 10 is a diagram illustrating the definition of the criterium of thecardiac frequency FC;

FIG. 11 is a double graphic showing the position of the synchro QRSimpulses to implement the analysis criterium called "arrhythmiacriterium";

FIG. 12 is a diagram illustrating the definition of the analysiscriterium called "arrhythmia criterium";

FIG. 13 is a composite diagram showing the weighting scales associatedwith the three principal tests;

FIG. 14 is a composite diagram showing the weighting scales associatedwith the four tests of the improved procedure;

FIG. 15 is the diagram illustrating the chronology of the events over aperiod of analysis and measurement formed by the two successive andjuxtaposed basic periods TA and TB;

FIG. 16 is the flow chart of the algorithm of the three successiveprincipal tests of the procedure according to the invention;

FIG. 17 is the flow chart of the logarithm of the four successive testsof the improved procedure according to the invention;

FIG. 18 is the flow chart continued from the algorithm according to thebasic embodiment improved with four tests when there is no alarm ordetection in progress;

FIG. 19 is the flow chart continued from the algorithm according to thebasic embodiment improved with four tests when there is an alarm or adetection in progress;

FIG. 20 is a functional synoptic diagram of the equipment implementingthe procedure according to the invention;

FIG. 21 is the diagram of the principle of the detector of the QRScomplexes and the formation of the synchro QRS impulse.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preliminary to the detailed description of the present invention, wewill now clarify the different concepts and definitions useful for aclear and good understanding of the description made hereafter.

The electrocardiographic signal transduced by a electrocardiogram,abbreviated ECG is sensed from the body of the patient by externalelectrodes in contact with the skin. If the defibrillation electrodesare adhesive, they may be used to sense the ECG signal.

The electrocardiographic signals of a healthy heart during normalactivity are repetitive and display a known repetitive waveformconstituted by several segments whose characteristic points areconventionally called P, Q, R, S and T, which are represented in FIG. 1.

The wave P corresponds to the depolarization of the auricles. Theinterval PQ represents the auriculo-ventricular conduction time. The QRScomplex corresponds to the ventricular depolarization (propagation inthe ventricles). The repolarization of the ventricles happens from S toT (segment ST) and during the wave T.

The QRS complex is one of the characteristic elements of anelectrocardiogram of normal cardiac activity. It will be used in theprocedure described hereinafter.

Synchro impulse QRS

The term "synchro impulse QRS" designates the impulse formed from thereal QRS complex by comparison with a threshold of fixed or variablevalue, for example variable in the case of the application envisionedhere.

Its role consists in showing the existence of a QRS complex or of a verysimilar neighboring waveform.

In addition, it constitutes a temporal reference for the triggering ofthe defibrillation shock in case of ventricular tachycardia.

Interbeating

The term "interbeating", abbreviated "Ti", is attributed to the durationseparating two synchro QRS impulses.

PACE

By convention, the term PACE signifies the inhibition of the stimulationimpulse.

As it appears in the electrocardiograms represented in FIGS. 4 and 5,the electrocardiogram signals characteristic of fibrillation andventricular tachycardia reveal themselves by a complete loss of thereproducible and periodic characteristic.

In regard to the fibrillation, the arrhythmic and random appearance ofthe signal is to be noted.

In contrast, ventricular tachycardia ECG signals show a high frequencypseudo-periodicity.

The procedure to monitor, to detect and to recognize a ventricularfibrillation or ventricular tachycardia condition from aelectrocardiographic signal according to the invention follows from thegeneral inventive idea consisting of preprocessing, digitizing theelectrocardiographic signals after a division according to apredetermined frequency, measuring from these signals valuescorresponding to the three criteria of zero, of cardiac frequency, ofarrhythmia, periodically allocating variable probability parameters tothese values representative of these three criteria, as a function oftheir levels taken from the weighting scale specific to each criteriaduring two consecutive elementary analysis periods and making themeasurements on each basic period correspond to a basic probability bythe weighting scales, each basic probability of each period being addedto the preceding one to form an overall probability as a function ofthese criteria to recognize, according to a given probability factor, ahazardous pathological condition and to trigger an alarm.

The procedure may be carried out by an additional criteria specific toventricular tachycardia.

After a conventional acquisition phase, carried out by conventionalmonitors, the ECG signals undergo an analog preprocessing by a filteringin a 1-40 Hz bandpass filter with suppression of the DC component. Thisfiltering essentially rids signals of parasitics and harmonic componentshindering the processing of the signals. The filtering is followed by anautomatic gain control AGC in such a manner as to always present the ECGsignal to the analog to digital converter ADC at full scale.

The analog signals are then sampled and converted into digital signalsin the ADC at a sampling frequency of 250 Hz during an overall analysisof duration D, for example 8 seconds, formed by two successive samplingand analysis basic periods TA and TB, for example, of a duration of 4seconds each, thus corresponding to 1.000 samples each. The automaticgain control AGC is an optimal analysis of the maximum value, whose goalis to always use the full scale of the converter when carrying out thedigital signal conversion step.

It is to be understood that by automatic gain control, abbreviated AGC,connected to the analog/digital converter ADC, an operation is meantwhich consists in using the maximum amplitude of the EGC signal as afull scale value of the converter.

In this manner, whatever the maximum amplitude of the ECG signal may be,the same maximum digital value (full scale) will be used to have ausable signal available in all cases.

Everything happens just as if the converter was adapting itself to theamplitude of the ECG signal.

For example, a QRS amplitude of 2 volts will be decomposed into 256equidistant levels, and 2 volts will correspond to the full digitalscale. According to the targeted automatic gain control, a maximum QRSamplitude of 2 volts will have the same maximum digital value as amaximum amplitude of 1 volt, the intervening values undergoing aproportional conversion.

Moreover, it is known that the preprocessed ECG analog signal has ausual amplitude situated, according to the patient, between 0.2 mV and 5mV. It is also known that for the small amplitudes around 0.2 mV, theECG signal is not adequately usable. It is necessary to allow for aninhibition signal of the detector, abbreviated LIMIT in FIG. 20, whichvalidates the alarm, thus signalling the non-possibility of detection.

Concurrently with the analog preprocessing and the digitization, theanalog signals output from the acquisition stage undergo a detection ofthe "QRS" complex in view of forming the synchro QRS impulse, as will bedescribed hereinafter.

Formation of the Synchro Impulse

The synchro QRS impulse is formed by a QRS detector constituted by thefollowing modules represented in FIG. 21:

DESCRIPTION

    ______________________________________                                        DESCRIPTION          FIG. 21 LABEL                                            ______________________________________                                        frequency of 100 HZ and a gain of 1.500                                                            FILTER GAIN 100 Hz                                       bandpass filter centered on 18 Hz                                                                  BANDPASS 6 Hz                                            absolute value module                                                                              ABSOLUTE VALUE                                           threshold/peak module                                                                              THRESHOLD/PEAK                                           comparator module    COMP                                                     impulse trigger      MONOSTABLE                                               ______________________________________                                    

The QRS complex detector is based on the analysis of the response of abandpass filter of 18 Hz of width 6 Hz. It is the absolute value of thesignal that is analyzed. If this absolute value exceeds a threshold thatis a function of the peak amplitude of the last QRS complex and a fixedthreshold, a synchro QRS impulse is emitted indicating by its presencethat the QRS complex is recognized.

In this manner, the presence of the synchro QRS impulses evidences theexistence of the QRS complex in the ECG signal analyzed.

The digital signals output from the analog and digital preprocessingstage and from the QRS detection stage are processed in a digitalprocessing unit which consists in various steps, of calculation anddigital analysis stages with respect to certain predetermined criteriaand variable according to specific sequences described hereinafter,analyses which lead to the recognition of a hazardous pathologicalcondition according to a given probability, determined by said criteriabut modifiable, and to the manual or automatic triggering of an alarm.

The selection of the criteria usable for the recognition of hazardouscardiac pathological condition results from much effort and many trials.

To recognize a ventricular fibrillation condition, the method and theutilized selected criteria are outlined hereinafter:

the analysis is carried out on samples of duration D decomposed in twojuxtaposed successive periods TA and TB of 4 seconds each;

the three essential criteria are: a criterium "of zeros", a criterium of"cardiac frequency" FC, and a criterium "of arrythmia" RR;

a rapid ventricular tachycardia criterium is added to increase thesensitivity and the reliability of the detection for this cardiacpathology;

the definition of these criteria are such that they are not uniquelyTRUE or FALSE but may have intermediate states.

After a basic analysis period TA or TB, for example 4 seconds, the valueof the basic probability worked out over this period of a ventricularfibrillation case PFV is incremented by adding the basic probability ofthe immediately preceding period APFV to determine an overallprobability linked to the duration D of two juxtaposed analysis periodsTA and TB. This overall probability: PGV=PFV+APFV is used to trigger thealarm.

To avoid abnormally short sequence or artifacts, it is the sum of thisventricular fibrillation probability PFV and the immediately precedingventricular fibrillation probability APFV calculated over the precedingperiod TA which will determine the triggering of the alarm.

To properly understand the following, the three criteria used, meaningcriterium of zeros Z, criterium of cardiac frequency FC, criterium ofarrythmia RR and a fourth optional criterium, with the aide of FIGS. 9to 14 will now be defined in a simple manner.

1. The Criterium of Zeros "Z"

The selection of this criterium was guided by the followingconsiderations.

The statistical study of normal cardiac activity has allowed us tonotice that, in an ECG, 60% of the points are located at a level belowthe + or -20% of the maximum value of the normal ECG (see FIG. 9). Thecounting of all of these signals gives an idea of the morphology of thesignal.

This criterium has been further improved in the following manner:

the maximum of the digital ECG always corresponds to the full scale ofthe conversion thanks to the automatic gain control AGC;

a threshold established at + or -20% of the maximum allows thesuppression of noise for the signals of weak amplitudes and stronglyattenuates the effect of parasitic signals, telephonic waves andradioelectric waves;

a lower limit (for example of 0.2 mV), under which no processing may bemade, validates the detection;

this criterium is not true or false but takes in consideration a certainnumber of values as a function of the number of zeros counted, thesevalues having been statistically defined.

With over 70% of the values close to zero, the probability of having anormal ECG is null. From 70 to 50%, the morphology is different from anormal sinusoidal rhythm and an emergency condition is probable. Under50%, the probability is high.

The criterium of zeros implements the counting of the number of sampledpoints whose level is close to zero. The sampled points that are calledclose to zero are those whose value is less than + or -20% of themaximum of the ECG, because in the case of ventricular fibrillation FVand ventricular tachycardia TV, the number of points close to zerobecomes low.

The criterium of zeros is precisely and mathematically defined in thefollowing manner:

It relates to the percentage of the number of sampled points during abasic analysis period, whose voltage level is situated at + or -20% ofthe maximum voltage level of the ECG relative to the total number ofsampled points that are less than 50% of the total number (FIG. 9).

This value is defined by Z.

The zero criterium gives an idea of the width of the QRS complex.

Example

normal ECG: a Z value greater than 60% is found';

TV and FV correspond to a Z value less than 50%.

2. The cardiac frequency criterium "FC"

It principally concerns ventricular tachycardias.

It is defined by the following formula:

    FC=60×(N+1)/(T+2)

where

N=number of synchro QRS impulses counted during a reference period;

T=duration between the end of the reference period and the next synchroQRS impulse (FIG. 10).

Application example of the formula:

Three synchro impulses are counted during two seconds (reference period)and the next synchro impulse arrives after one second.

N=3 and T=1

By applying the above formulation, it is found that:

FC=80 beats per minute

This cardiac frequency is to be compared with an actual cardiacfrequency of 80 beats per minute. In principle, this calculated cardiacfrequency is equal to the actual cardiac frequency.

Although it is difficult to define a threshold under which an alarm mustsound, the increasing probability scale is the following:

from 150 to 200 b/mn the probability is low

from 200 to 300 b/mn, it increases;

beyond 300 b/mn, it is greatest.

3. The arrythmia criterium "RR"

The arrythmia criterium is evidenced by a degree of arrythmia RR.

It characterizes the random phenomena of ventricular fibrillation, theother cardiac rhythms being fairly regular.

The degree of arrythmia is defined as the relationship in percentage ofthe number of interbeatings out of ten from the last ten interbeatingswhose relative value are located at or -30% of the average interbeatingvalue, abbreviated "average Ti" (FIG. 12).

Examples The Ventricular Fibrillation FV

It is characterized by an irregular signal. If the arrythmia signal isweak, for example greatly inferior to 50%, it will engender a highcoefficient of ventricular fibrillation probability PFV.

The Ventricular Tachycardia

It is characterized by a regular signal. If the degree of arrythmia ishigh, for example greater than 50%, it will engender a low coefficientof ventricular fibrillation probability PFV and conversely a highprobability of ventricular tachycardia.

This criterium allows the discrimination of ventricular fibrillationfrom its essentially random character with respect to other cardiacfrequency pathologies, of fairly regular nature.

4. The fourth criterium "PTV"

To increase the sensitivity of the detector for rapid ventriculartachycardia, a fourth criterium is provided for an improved embodiment.

According to this criterium, the three following conditions must besimultaneously satisfied:

criterium of zeros "Z" less than 50%;

cardiac frequency greater than 140 b/mn;

degree of arrythmia RR greater than 75%;

These three conditions are systematically satisfied for the rapidventricular tachycardia that is sought to be detected.

This criterium is implemented by the fourth test. It is totallytransparent to the ventricular fibrillation which presents other typicalcharacteristics.

This test leads to increasing the probability of a certain weight forrapid ventricular tachycardia.

To utilize another temporal reference, the analysis of the arrythmia isdone at the end of four seconds and over the ten last intervalsseparating the two successive synchro QRS signals, these intervals beingcalled "interbeating time" or Ti.

After having calculated the average of these times Ti, each interbeatingis analyzed and compared to the average. A tolerance of 30% around thisaverage determines the number of times Ti that are close to the average,this number corresponds to the degree or criterium of arrythmia.

Statistically, with eight out of ten interbeating intervals around 30%of the average, the rhythm is considered as regular, below that, therhythm is irregular and may correspond to an emergency condition.

For this criterium, the auricular fibrillations have a large coefficientbut do not trigger alarms, these conditions are thus not taken intoaccount by the detector according to the invention.

The ECG signals that are sampled and digitized over a total duration Dof two consecutive sampling and analysis periods are numericallyprocessed in a microprocessor utilized as a microcalculator according tothe chosen criteria earlier mentioned, of zero Z, of cardiac frequencyFC, of arrythmia RR and for the improved embodiment according to aspecific criteria of ventricular tachycardia PTV.

The 1.000 samples of each basic successive period TA and TB of 4 secondseach are accounted for and analyzed at the end of each period withrespect to the chosen criteria.

Therefore:

a value "Z" is detected to be utilized by the test of the zeros;

the value "FC" representative of the cardiac frequency is worked out;

the value "RR" representative of the arrythmia is calculated;

each measurement value over a basic period is periodically attributed aweighting given by a weighting scale specific to each test to form abasic probability;

the basic probabilities are added over two successive analysis periodsTA and TB to find a deciding overall probability linked to an analysisduration which will trigger or not the alarm according to its positionwith respect to a predetermined threshold.

The recognition of a ventricular fibrillation or ventricular tachycardiacondition is continuously carried out from the analysis of the threecriteria or of the four criteria (improved embodiment) over the totalduration of analysis, eight seconds as in the example. It is agreed thatif the overall probability PFG or PFVG (improved embodiment) of PFV andAPFV is greater than 11, the ventricular fibrillation or ventriculartachycardia state is recognized by the microcontroller and an alarm istriggered.

However, 10 synchros are necessary to detect an emergency physiologicalcondition.

The end of the detection is obtained for two successive values less than5 and the alarm stops (FIG. 19).

The procedure may be further carried out by an additional stage whichconsists in a stage of "shock proposal" which is evidenced by thecharging of the defibrillation capacitors and the preparation of theequipment which delivers the defibrillation electric shock so theoperator may intervene even more rapidly on the patient.

According to another embodiment of the procedure, the preprocessingstage may be cancelled inasmuch as the acquisition stage of the ECGalready delivers an adapted bandpass signal (FIG. 8).

An example will be given hereinafter of the weighting scales of the testutilized as well as a description of the functioning in the twoconditions of fibrillation and ventricular tachycardia.

The FIGS. 13 and 14 illustrate the weighting scales of the tests used inthe two embodiments of the procedure, which are, as already indicated,the following: test of zero (abbreviated: zero test), cardiac frequencytest (abbreviated: FC test), arrythmia test (abbreviated: RR test) andaccording to an improved embodiment an additional test of theventricular tachycardia probability (abbreviated: PTV test).

The goal of these figures is to clearly show the weighting coefficientsattributed to the different values according to their level to determinea ventricular fibrillation probability PFV, after two successiveanalysis periods TA and TB, the immediately preceding analysis periodprobability being determined in the same manner and referenced by aAPFV.

For each test, a weighting coefficient is allocated, according to theamplitude zone where the result of the weighting scale of this test isfound.

Test of the Zeroes

The value of the probability is attributed, by the weighting scale ofthe test of the zeros, a variable weighting coefficient equal forexample to:

4 if the number Z during the analysis period is located between 0% and50%;

2 if the number Z during the analysis period is located between 50% and55%;

1 if the number Z during the analysis period is located between 55% and70%;

0 if the number Z during the analysis period is located between 70% and100%;

3 beyond that period.

Cardiac Frequency Test FC

The value of the probability is attributed, by the weighting scale ofthe cardiac frequency FC test, a variable weighting coefficient equalfor example to:

0 if the cardiac frequency during an analysis period is less than 140b/mn (null probability);

1 if the cardiac frequency during the analysis period is located between140 and 200 b/mn (low probability);

2 if the cardiac frequency during the analysis period is located between200 and 300 b/mn (average probability);

3 beyond (high probability).

Arrythmia Test RR

The value representing the probability is attributed, by the weightingscale of the arrythmia test RR, a variable weighting coefficient equalfor example to:

3 if the degree of arrythmia during the analysis period is less than orequal to 50%;

2 if the degree of arrythmia during the analysis period is locatedbetween 55% and 65%;

1 if the degree of arrythmia during the period of analysis is locatedbetween 65% and 75%;

0 if the degree of arrythmia during the period of analysis is locatedbetween 75% and 100%.

To avoid being limited by the specified numbers, it could as well besaid that in such or such zone of values, the probability is null, low,average or large.

Fourth Test "PTV"

To increase the sensitivity and the reliability of the detection in thecase of ventricular tachycardia, an additional test is carried out saidventricular tachycardia probability test (PTV) (FIG. 14).

This additional test consists in systematically verifying if the threefollowing conditions are simultaneously satisfied:

few zero values denominated Z;

regular cardiac frequency determined by a low RR value;

the cardiac frequency is greater than 140 beats per minute.

If these conditions are not simultaneously met, the probability of zerois increased (the test is transparent). This is in the case ofventricular fibrillation.

If these conditions are simultaneously met, the basic probability isincreased by a low weight (for example 1) to generate a new overallprobability PFTVG=PFTV+APFTV (FIGS. 14, 18 and 19).

If necessary, a new limit of the probability causing the triggering ofthe alarm may be determined by increasing it for example by one unit.

For a better comprehension of the procedure of the implementingequipment, an example of detection of ventricular fibrillation and anexample of detection of ventricular tachycardia using the improvedembodiment (threshold of probability equal to 11) will be describedhereinafter.

A pathological state is assumed to occur after several minutes of normalactivity of the heart of the patient.

Ventricular Fibrillation

The sudden change in the nature of the signals is immediately evidencedby irregular synchro QRS impulses.

The test of the zeroes causes the weighting of this criterium totransition from a value of 0 to a value of 4 due to the largerwaveforms.

The FC test will cause the value to exceed 200 beats per minute or incertain cases no QRS complex impulse will be generated during a durationnecessarily greater than 2 seconds.

The RR test allocates a maximum weighting value because of the randomcharacter of the responses of the QRS detector.

A probability value for an analysis period will result from this test ofPFTV+APFTV=9 for example, this sum becoming equal to 18 upon adding theweighting value from the next basic analysis period TA or TB. If thisprobability is greater than 11, a ventricular fibrillation condition FVwill be recognized.

Rapid Ventricular Tachycardia

The change of the ECG signals to a typical deformation and anaccelerated tachycardia rhythm is evidenced by a rapid rhythm with largeQRS complexes.

This detection has been voluntarily limited to a rhythm greater than 140beats per minute because the danger only appears above this heart rate.

In this manner, if this frequency is reached, the detector will react inthe following manner.

The criterium of zeros will allocate a weighting value of 4 due to thelarge QRS complexes.

The criterium FC will contribute a weighting value of at least 1.

The criterium RR will not contribute any increase in the probability.

To trigger the alarm, it is the additional test of ventriculartachycardia probability PTV that will add a value equal to 1 if all ofthe conditions of this test are met.

The number of the overall probability will be equal to 6 for a firstbasic analysis period TA and equal to double that value, meaningPFV+APFV=12 after the second basic period TB.

According to the probability threshold established at 11, this number 12being greater than 11, the alarm will sound.

From the digitized ECG signal, the magnitudes Z, FC and RR areestablished corresponding to the three criteria, meaning in conformitywith the definitions specified hereinafter.

Z Magnitude

The magnitude Z to be used with the zero test is established by acomparison, followed by a counting of all of the sampled points whosevoltage value corresponds to the value of the definition of the zerocriteria, meaning two whose voltage level is located at + or -20% of themaximum voltage level of the ECG relative to the total number of sampledpoints.

Comparative measures allow the isolation of the number of points definedabove; it is then necessary to give it the relative desired valuecorresponding to its definition.

These operations are carried out in the digital and calculationprocessing unit.

This magnitude is then put to the zero test according to the weightingscale corresponding to this criterium represented in FIGS. 13 and 14 toestablish a basic probability according to the general algorithm.

Magnitude FC

This magnitude FC to be used with the cardiac frequency test is workedout by counting the number N of synchro QRS impulses during a givenreference period. The duration T between the end of the reference periodand the next synchro QRS impulse is accounted for as well.

The calculator establishes the cardiac frequency according to theformula:

    FC=60×(N+1)/(T+2)

This magnitude is then put to the cardiac frequency test according tothe weighting scale specific to this criterium represented in FIGS. 13and 14 to establish a basic probability according to the generalalgorithm.

Magnitude RR

This magnitude RR representing the degree of arrythmia corresponds tothe definition specified hereinafter.

Ten interbeatings Ti are counted from the synchro QRS impulse. Theaverage of these ten last interbeatings is calculated. The number ofinterbeatings are counted whose value is located at + or -30% of theaverage and the percentage of this number of interbeatings is calculatedwith respect to the total number of these interbeatings Ti over theperiod of calculation. By definition, this number is equal to ten.

This magnitude is then put to the arrythmia test according to aweighting scale specific to this criterium represented in FIGS. 13 and14 to establish a basic probability according to the general algorithm.

General Algorithm

The general algorithm accounts for all of the contemplated tests and ofthe final algorithm intended for the taking of the decision.

This algorithm is represented in FIGS. 16, 17, 18 and 19.

It is described almost completely at all of the basic periods TA or TB.

For a proper understanding, it is necessary to refer to FIG. 15.

This algorithm accounts for the progress of the systematic operations ofthe procedure beyond the establishment of the magnitudes resulting frommeasurements comprising the transition to different weighting scales ofthe test.

The algorithm begins by a reinitialization instruction after each basicanalysis period TA or TB to describe it another time.

The establishment of the magnitudes Z, FC and RR is continuously carriedout, on each basic period, these numbers or magnitudes are available atthe end of each basic period TA and TB.

At the end of each of these periods, the algorithm is completelydetermined.

The algorithm is carried out anew each time that new values areavailable to establish a new overall probability.

At the end of two successive basic periods TA and TB, the two basicprobabilities APFV or APFTV and PFV or PFTV are added in a summer toestablish an overall probability which will determine a recognitionstate and will propose a decision to defibrillate.

The goal of the flow chart of the algorithm is to show the detail ofthese tests.

These tests are the three principal tests following: test of zeros, FCtest, RR test for the variant, to which a ventricular tachycardiaprobability test (PTV test) is added for the actual complete procedurewith improved embodiment.

This last test is transparent for a ventricular defibrillation, becausethe added value is null.

In contrast, this test increases the overall probability in differentproportions according to the preceding criteria examined another timeindividually and taken into account simultaneously.

A new overall probability PGTV is in this manner defined which is thefinal probability after the examination of all of the criteria and thepassage of all of the tests on two successive analysis basic periods TAand TB. It is equal to the sum of the two new elementary probabilitiesAPFTV and PFTV which are the basic probabilities after the final testPTV:

    PGTV=APFTV+PFTV

The rest of the general algorithm which is applicable as well to thebasic embodiment and in the case of the improved embodiment implementingthe fourth test in reference to FIGS. 18 and 19 will now be examined.

The goal of the first algorithm (FIG. 18) is to implement an ultimatetest relative to the rapid ventricular tachycardia (FC greater than 140b/mn) that is sought to be detected in the most certain manner possible.

The goal of the second algorithm (FIG. 19) is to monitor the case of analarm and to determine if the alarm should be maintained or stopped ifit has been triggered.

Concerning the first algorithm, the limit of the chosen probability,here the number 11, being exceeded, the case of an alarm is acquired.Before triggering the alarm, a last ventricular tachycardia test iscarried out. This test concerns the two following alternatives:

1) the ventricular fibrillation probability FV is that of a case whereRR is less or equal to 55% (low degree of arrythmia)

2) one interbeating duration in ten is longer than two seconds with alater passing of the control if the cardiac frequency is greater than140 b/mn.

This last test has appeared to be necessary in the cases where it iscertain that the probability of ventricular fibrillation is not large orin the case of an ineffectual detection of the QRS (the QRS complex isno longer recognized in the signal).

In this manner, if one or the other of the alternative conditions above:

is met, the alarm is allowed to sound;

is not met, it is determined whether the cardiac frequency is greaterthan 140 b/mn:

if the cardiac frequency is less than this limit, the alarm is notvalidated and the algorithm returns to its beginning

if the cardiac frequency is greater than this limit, the alarm istriggered on this confirmation.

In the case of an alarm or of a detection in progress, the decision tomaintain or to stop the alarm results from the algorithm represented inFIG. 19.

If over two successive measurement and analysis basic periods TA and TB,the probability is less than 5, the given alarm is then stopped and thealgorithm proceeds as in FIG. 18.

In the contrary case, the alarm is maintained and the algorithm returnsto the beginning of the general algorithm.

It is proper to note here that the measurements and analysis areperiodically and continuously carried out. This means there is aconstant monitoring. The least modification sensed by the detectoraccording to the invention of the cardiac state of the patient willquasi instantaneously or not (depending on the result of the tests)modify the alarm state in which it finds itself.

It is also planned to carry out an additional and confirming analysisbefore the automatically triggering the alarm.

After taking the ECG signal on the patient, an amplification-filteringstep is carried out followed by an analog preprocessing, an automaticgain control AGC and an analog/digital conversion in an ADC converter.

Concurrent to an analog preprocessing and AGC followed by ADC, the QRScomplex is detected and a synchro QRS impulse is formed.

These informations, signals and data are entered in a microcalculator,for example of 8 bits, for various digital calculation and analysisprocessing with respect to the test on the values Z, FC, RR, test PTV,in view of emitting an alarm in the case of a recognition of thepathological cardiac condition and the systematic preparation of thedefibrillation shock by the charging of the defibrillation capacitor ofthe associated fibrillator.

According to the basic embodiment, the decision to shock belongs to themonitoring physician or equivalent personnel (FIG. 6).

According to a more complete embodiment, the decision to shock isautomatically taken and given as soon as an additional analysis showsthat the pathological state remains (FIG. 7).

The implementation means of the procedure will now be described with theaid of FIGS. 20 and 21.

The acquisition circuit receives the signals gathered by the electrodesplaced on the patient.

The function of the acquisition circuit which may be a part of anexisting monitor is to deliver from a signal superimposed with noise andparasitic signals, an ECG signal of 1 to 5 volts with a passbandpredefined by the limits from 0.05 to 100 Hz. The means used areconventionally and already utilized by other medical monitoringequipment.

A visualization by screen and a printer for the graphic version are apart of the acquisition circuit.

The detector itself according to the invention essentially comprisespreprocessing means of the signal furnished by the acquisition circuit,digital preprocessing means and an alarm device.

The analog preprocessing means are composed of an analog-digitalconverter ADC preceded, in the embodiment represented in FIG. 20, by afilter whose filtering limits 1 and 40 Hz approximately, have beenjustified above. The goal of this filter is to allow the user to adaptthe output pass band of the acquisition circuit to the input frequencieslimited to 1 and 40 Hz of the analog-digital converter.

According to another embodiment, the standard acquisition circuit abovemay be replaced by an acquisition circuit delivering a signal whose passband is already adapted, in this case, the preprocessing means would notcomprise a filter. Eventually, one or several means to suppress thesignals output from the detectors or equipment other than theventricular fibrillation and ventricular tachycardia detectors accordingto the invention may be foreseen, which signals could perturb the ECGsignal. As non-limiting example, a "switch" function to eliminate theimpulses generated by a cardiac stimulator have been symbolicallyrepresented in FIG. 20 with the reference PACE.

The preprocessing means are essentially comprised of:

a analog to digital converter abbreviated ADC

an automatic gain control abbreviated AGC

a peak signal value optimizer.

The peak signal detector is a conventional electronic circuit comprisinga diode charging a peak value capacitor, if the amplitude of thepreprocessed signal is larger than the amplitude charged in thecapacitor. This capacitor is chosen with a ten millisecond chargingconstant to avoid taking into account a large amplitude parasitic signaland with a discharge time constant of several seconds (4 or 8 forexample) to allow to follow the maximum of the signal if its amplitudediminishes.

The automatic gain controller AGC always allows the utilization of thefull scale of the analog digital converter ADC. As specified, theabsolute value of the maximum amplitude of the preprocessed analogsignal has been chosen as conversion reference.

The processing means itself is based on a microprocessor, for example amicroprocessor of the INTEL 8051 (8 bit) type utilized asmicrocalculator which necessitates few peripheral components: afrequency setting quartz oscillator, an EPROM containing the digitalprocessing program, a working RAM memory and a "watchdog" autocontrolmeans. The digital processing program is that which has been describedearlier for the procedure.

In parallel with the preprocessing means, a QRS complex detector isplanned which is especially conceived to deliver to the microcalculatoror to the digital processing unit a digital signal in synchronism witheach QRS complex detected on the ECG of the patient.

Reference is now made to FIG. 21 for the description of the QRS complexdetector.

A pass band filter of 18 Hz, of width 6 Hz eliminates the differentcomponents of the QRS complex. This complex may be positive or negativeaccording to the derivation of the electrocardiogram, the rectifyingmeans allowing to take into account the absolute value of the responseof the pass band filter 18 Hz to always detect the first positiveimpulse.

The detection of the complex is then carried out with the aid of acomparator COMP by exceeding a threshold, which is variable, and dependson the maximum amplitude of the last detected QRS complex, of theelapsed time since this last QRS, and of a fixed value (which is aminimum detection value). A compromise has been found between thesethree data which are essentially charging and discharging times of thecapacitor. The signal output from the comparator is a digital signalindicating the presence or absence of the QRS complex, it is thentreated by a monostable vibrator, of refractory period on the order of150 to 200 ms which prevents the double counting for the large complexesand which allows a synchronization signal up to cardiac frequenciesgreater than 300 pulsations per minute to be delivered.

According to an embodiment, the input signal of the QRS detector istaken at the input of the preprocessing filter. This arrangement is notlimiting, as a signal originating from the adhesive defibrillationelectrodes may be taken directly on the acquisition circuit.

The ventricular fibrillation and tachycardia detector additionallycomprise:

a technical alarm device to validate the alarm in the case of an anomalyin the acquisition circuit, preprocessing, or processing, for example,when an electrode has detached from the patient. This type of alarm isreferenced in the figure by "electrode defect".

The alarm device itself consists in an audible alarm and/or a visualmessage managed for example by the acquisition circuit but validated bythe output digital signal of the microcalculator.

For the semiautomatic embodiment of the detector, the digital outputsignal of the microcalculator also validates the charging means whosefunction is to place an associated defibrillator in a functioning stateas soon as the operator gives it the command impulse. This embodiment isrepresented in dashed lines in FIG. 20.

We claim:
 1. Procedure to monitor, detect, and to recognize a hazardouspathological cardiac condition in view of applying an electricdefibrillation shock, wherein said procedure comprises the step of:a)acquiring an analog ECG signal from transducers attached to a patient'sbody; b) processing said analog ECG signal in an analog preprocessingunit; c) continuously sampling and digitizing said analog ECG signalover a measurement and analysis period D, said period D consisting oftwo identical basic periods TA and TB; d) establishing from saiddigitized ECG signals values Z, FC and RR corresponding to resultsobtained by applying said digitized ECG signal to a zero test, a cardiacfrequency test, and degree of arrythmia test, respectively; e) forming,from said analog ECG signal, synchro QRS complex impulses when a cardiacrhythm of said patient exhibits QRS complexes; f) digitally processingsaid Z, FC and RR values over two successive measurement analysisperiods TA and TB; g) obtaining, from said digitally processed Z, FC andRR values, a basic probability value for each basic period TA and TB,said basic probability value depending upon where said Z, FC and RRvalues fit within a weighting scale proper to each of said Z, FC and RRvalues; h) summing said basic probability values obtained over saidbasic period TB with said basic probability value obtained over saidprevious basic period TA; i) obtaining, from said summed basicprobability values, an overall probability value; j) repeating saidsteps a)-i) if said overall probability value does not exceed a setthreshold; k) triggering an emergency alarm and charging an electricdefibrillator if said overall probability value equals or exceeds saidthreshold; l) upon validation of said probability of recognition of apathological cardiac condition, discharging said electric defibrillatoronto said patient in an attempt to stabilize said cardiac rhythm. 2.Procedure according to claim 1, wherein said ECG signal is sampled at asampling frequency of 250 Hz and each measurement and analysis period TAand TB is 4 seconds.
 3. Procedure according to claim 1, wherein saidsynchro QRS impulse is formed by:inputting said ECG signal into anamplified filter having a 100 Hz cutoff frequency; inputting an outputof said amplified filter into a bandpass filter centered on 18 Hz;isolating an absolute value of an output of said bandpass filter;comparing said absolute value to a variable threshold, a peak amplitudeof a last detected QRS complex, and a fixed, minimum detection value;outputting from said comparator a synchro QRS impulse calibrated inamplitude and in duration, said synchro QRS impulse indicating apresence or absence of said QRS complex in said cardiac rhythm of saidpatient.
 4. Procedure according to claim 1, wherein said Z values aredefined as a percentage of a number of sampled points during ameasurement and analysis period whose voltage level is located within20% of a maximum voltage level of said ECG signal with respect to atotal number of sampled points less than 50% of the total number, andestablishing a probability value by allocating to said Z values, througha probability scale of a test of zeros, a variable weighting coefficientequal to:4 if said Z value during said measurement and analysis periodis located between 0% and 50%; 2 if said Z value during said measurementand analysis period is located between 50% and 55%; 1 if said Z valueduring said measurement and analysis period is located between 55% and70%; 0 if said Z value during said measurement and analysis period islocated between 70% and 100%; 3if said number Z during said measurementand analysis period is above 100%.
 5. Procedure according to claim 1,wherein said FC values of cardiac frequency are defined by the followingformula:

    FC=60×(N+1)/(T+2)

wherein, N=number of synchro QRS impulses counted during a referenceperiod; T=duration between an end of said reference period and a nextsynchro QRS impulse; and wherein a basic probability value isestablished by allocating to said FC value, by a probability scale ofsaid cardiac frequency FC test, a variable weighting coefficient equalto:0 if said cardiac frequency during said measurement and analysisperiod is less than 140 beats per minute, thus indicating a nullprobability; 1 if said cardiac frequency during said measurement andanalysis period is located between 140 and 200 beats per minute, thusindicating a weak probability; 2 if said cardiac frequency during saidmeasurement and analysis period is located between 200 and 300 beats perminute, thus indicating an average probability; 3 if said cardiacfrequency during said measurement and analysis period is above 300 beatsper minute, thus indicating a strong probability.
 6. Procedure accordingto claim 1, wherein said RR values of degree of arrythmia are defined asbeing a relation in percentage points between a number of interbeatingsin ten from a test last interbeatings which are located at + or -30% ofan average interbeating value Ti, and wherein a basic probability isestablished by allocating to said value RR, through a weighting scale ofsaid arrhythmia test RR, a variable weighting coefficient equal to:3 ifsaid degree of arrhythmia RR during said measurement and analysis periodis less than or equal to 50%; 2 if said degree of arrhythmia RR duringsaid measurement and analysis period is located between 55% and 65%; 1if said degree of arrhythmia RR during said measurement and analysisperiod is located between 65% and 75%; 0 if said degree of arrhythmia RRduring said measurement and analysis period is located between 75% and100%.
 7. Procedure according to claim 1, wherein an additionalventricular tachycardia probability PTV is established according towhich an additional probability weight is added if the followingconditions are simultaneously met:a possibility of ventricularfibrillation is such that said RR value is less than or equal to 55%;one interbeating time Ti in ten is greater than 2 seconds.
 8. Procedureaccording to claim 1, wherein when said emergency alarm is triggered,said procedure further proceeds to carry out a final test comprising thesteps of:verifying that the degree of arrhythmia is less than or equalto 55%; if said interbeating time is greater than at least 2 seconds,validating said emergency alarm if a positive response is obtained andalso validating said emergency alarm if a negative response is obtainedand said cardiac frequency is greater than 140 beats per minute. 9.Procedure according to claim 1, wherein said emergency alarm ismaintained if said basic probabilities over two successive basic periodsTA and TB are each less than
 5. 10. Procedure according to claim 1,wherein said electric defibrillator is automatically put in a conditionof readiness to apply a defibrillation electric shock as soon as saidoverall probability value exceeds said set threshold.